2-Hydroxy-4-(methylthio)butyric acid is an analog of the essential amino acid 1-methionine, and it is an important compound for using for feed additive. As methods for production thereof, a method comprising adding methanethiol to acrolein to obtain 3-methylthiopropionaldehyde, reacting 3-methylthiopropionaldehyde obtained with hydrogen cyanide to obtain 2-hydroxy-4-methylthiobutyronitrile, and then hydrolyzing 2-hydroxy-4-methylthiobutyronitrile obtained with sulfuric acid has been known (e.g. U.S. Pat. No. 4,524,077).